Fault interrupting devices are designed to trip in response to the detection of a fault condition at an AC load. The fault condition can result when a person comes into contact with the hot side of the AC load and an earth ground, a situation that can result in serious injury. A ground fault circuit interrupter (GFCI) detects this condition by using a sense transformer to detect an imbalance between the currents flowing in the line and neutral conductors of the AC supply, as will occur when some of the current on the load hot side is being diverted to ground. When such an imbalance is detected, a relay or circuit breaker within the GFCI device is immediately tripped to an open condition, thereby removing all power from the load.
Many types of GFCI devices are also capable of being tripped not only by contact between the line side of the AC load and ground, but also by a connection between the neutral side of the AC load and ground. The latter type of connection, which may result from a defective load or from improper wiring, is potentially dangerous because it can prevent a conventional GFCI device from tripping at the required threshold level of differential current when a line-to-ground fault occurs.
Most GFCI devices provide some form of manual and/or self test operation to allow a user to insure the integrity of the GFCI protection device. For a manual test on a GFCI protection device, the user is required to press a test button which simulates a ground fault condition in a GFCI protection device, resulting in the contacts of the GFCI protection device opening. Existing self testing fault protection devices have been provided which have a self test function to obviate a user having to perform manual tests at various intervals of time (e.g., weekly, monthly, and so on). Many GFCI devices employ a GFCI integrated circuit or chip in the sensing circuit that processes data received from the sensing transformers and provides an output or trip signal that can be used to activate a gated device such as an SCR and energize a solenoid and open the contacts. A microprocessor, in turn, monitors outputs from the GFCI chip and SCR, among other components. As described in the above-referenced application Ser. No. 11/000,531, self-testing can be performed to test the integrity and operation of the GFCI integrated circuit (IC) or chip, the SCR and the solenoid without having to open the contacts and interrupt power to the load. The self test circuitry also comprises an indicator such as a light emitting diode (LED) for annunciating end of life (EOL) when the self test determines that the GFCI is no longer working effectively (e.g., the GFCI chip, the SCR or the solenoid are nonfunctional)
In existing GFCIs, a four diode bridge is generally used to supply power to the GFCI's components and, in particular, to both the GFCI chip and its associated circuitry (e.g., microcontroller, SCR and solenoid) and the self test circuitry. When the bridge shorts, a printed circuit board track can open, thereby removing power from both the core GFCI circuitry and the self test circuitry. Accordingly, no EOL indication is possible. A need therefore exists for a way to provide power to the self test circuitry when a PCB track opens as a result of a shorted bridge diode.
GFCI devices may be connected to fuse boxes or circuit breaker panels to provide central protection for the AC wiring throughout a commercial or residential structure. More commonly, however, GFCI devices are incorporated into electrical receptacles that are designed for installation at various locations within a building. A typical receptacle configuration is shown, for example, in U.S. Pat. No. 4,568,997, to Bienwald et al., the entire content of which is incorporated herein by reference.
A need also exists for a means to remove power from the face receptacle contacts and the load terminals when EOL occurs.